A three-part mold used in pressure and injection molding normally has two outer parts that sandwich an inner part. One of the outer parts carries the core or plug of the mold and the other outer part along with the inner part together form the outside of the mold. For demolding an injected or blown article it is normally necessary first to pull the plug or plugs out of the mold, then to separate the other two parts of the mold. Similarly on closing it is normally desired to insert the plug part on the one outer mold part into the inner mold part only after mating of the inner mold parts with the outer mold part.
Accordingly it is known to provide a latch arrangement on a three-part mold to ensure such sequential opening and closing. Such a latch arrangement is described in German patent publication No. 1,215,876. This arrangement has a pair of bars extending toward each other and each mounted on the respective one of the outer plates. These bars are pivotal and can engage a pin fixed on the inner plate and surrounded by a displaceable control unit. Control and locking surfaces on the bars interact with each other and with the pin and control slide to ensure the desired sequential functioning both during opening and closing.
The disadvantage of this known system is that the mechanism is relatively complex and must undergo quite some displacement during operation. As a result operation of the latch mechanism is relatively noisy. Furthermore such a latch mechanism is subject to considerable wear and is relatively expensive to manufacture.